does typespec support header on namespace/interface?

[sku0x20]

a header which should be included in all api calls and they are invalid without it.
eg. App-Version

[allenjzhang]

header is another property field that can only exist on models. Having said that, TypeSpec offers layered extensibility which you can further enhance/apply team/org level API patterns on top of lower level construct. For example, rest operations are built on lower http primitives. You can create custom operation/interface template to codify the inclusion of said header or others such as standard error response. To enforce the adherence of the org/team requirements, custom linter can be added if you publish these common patterns in a library.